The present invention relates to analytical apparatus and, in more particular, to analytical apparatus adaptable for use in analyzing highly toxic dioxin generatable from incinerators or else while offering measurabilities for a variety of kinds of materials including vapors as vaporized from dangerous objects such as explosives typically including nitro compounds and also agricultural chemicals containing therein chlorine and/or phosphorus elements.
Prior known approaches to dioxin analysis include a method for employing gas chromatography mass spectrometers using a high-resolution mass spectrometer of the magnetic sector type. This method is typically designed including the steps of preparing a mixture of dioxins as concentrated or enriched through complicated pre-processing processes, introducing the dioxin mixture into a gas chromatograph for separation, and then irradiating it with electron beams providing positively charged ions for detection by the high-resolution magnetic mass spectrometer. An advantage of this approach lies in an ability to perform qualitative analysis of dioxins (specifying the exact kind of a dioxin of interest by rendering determinable how many coupled chlorine elements it has, or alternatively which one of dibenzo-para-dioxin backbone and dibenzofuran backbone it has) on the basis of ion""s mass numbers detected, and also a capability to carry out a dioxin quantitative analysis based on ion intensities detected.
Another prior art technique for use in explosives detection instruments is shown in FIG. 18, which has been disclosed in xe2x80x9cORGANIC MASS SPECTROMETRY,xe2x80x9d Vol. 16, No. 6, 1981 at pp. 275-278. A method as taught thereby includes the steps of preparing dinitrobenzene dissolved in a chosen solvent such as methanol, letting it pass through a capillary 54 while simultaneously allowing a gas such as a nitrogen gas to flow in a pipe 55 coaxially provided to this capillary 54 for nebulization, and then generating a great amount of liquid drops 58. When this is done, the drops 58 generated are made finer by a heatup pipe 56 that is heated by its associated heater 57 while part of them becomes vaporized. Thereafter, the resultant vaporized molecules are guided into a negative corona discharge region which is associated with a corona discharging needle-like electrode 59 to thereby produce negatively charged ions or xe2x80x9canionsxe2x80x9d as to molecules of the sample under measurement, possibly due to electron addition effects and ion/molecule reaction activities.
The ions produced are then introduced for detection via a capillary into a mass analyzer unit 60, which may be a quadrupole mass spectrometer in high vacuum. With the prior art method also, it is possible, as in the method using the gas chromatograph mass spectrometer, to presume based on the mass numbers of detected ions what kinds of dangerous objects are present while at the same time enabling prediction of an amount of each dangerous object on the basis of ion intensity values detected.
The prior art dioxin analyzation using high-resolution magnetic-sector mass spectrometers has been designed to perform the intended analysis by positively ionizing dioxins through irradiation of electron beams thereonto. Unfortunately, this approach is encountered with several problems. One problem is that the detection sensitivity is relatively low due to the fact that the production efficiency of positive ions from dioxin molecules (ionization efficiency) stays lower than expected, which would in turn create the need for condensation or enrichment of dioxins at high degrees through complicated pre-processing processes prior to effectuation of the intended analyzation procedure. Another problem is that the need for such complicated and time-consuming preprocessing results in an increase in time duration while increasing costs therefor.
On the other hand the prior art explosives detection system is faced with a problem which follows. The expected detectability is hardly achievable in cases where samples of interest are less in amount. This can be said because in view of the fact that solid samples are dissolved in solvent such as methanol for introduction, the system is incapable of directly analyze vapors of such solid samples. Another reason considered is that nitro compounds in ion sources are inherently low in ionization efficiency resulting in difficulty of detection of such micro samples.
For example, see U.S. Pat. No. 4,580,440 (Apr. 8, 1986) entitled Method of Detecting a Contraband Substance and U.S. Pat. No. 4,718,268 (Jan. 12, 1998) entitled Method and Apparatus for Detecting a Contraband Substance.
Other prior art technique is disclosed in Tandem Mass Spectrometry , F. W. McLafferty ed., John Wiley and Sons, Inc., p353-370, 1983 and xe2x80x9cTRACE MONITORING BY TANDEM MASS SPECTROMETRYxe2x80x9d J. B.French, W. R.Davidson, N. M.Reid, and J. A. Buckley Sciex Corporation . This method as taught thereby includes the steps of generating ions of M and/or (M-COCl) by using atmospheric pressure chemical ionization method with positive mode. However, this prior art is faced with a problem that ionization efficiency of dioxins and their related compounds is low.
Other prior art technique is disclosed in U.S. Pat. No. 4,580,440. This method as taught thereby includes steps of chemical concentration process, that is, collecting particulates, rapidly heating said collected particulates for achieving high sensitivity. However, said chemical concentration process is time-consuming both for one measurement and continuous measurement.
Other prior art technique is disclosed in U.S. Pat. No. 4,718,268. This method as taught thereby includes steps of chemical concentration process, that is, collecting particulates, rapidly heating said collected particulates for achieving high sensitivity. However, said chemical cocentration process is time-consuming both for one measurement and continuous measurement.
To avoid the problems associated with the prior art the present invention provides an improved analytical apparatus, which is arranged including a sample introduction unit for introducing a gaseous sample to be measured, a corona discharge unit for letting the introduced gas sample undergo corona discharge of the negative polarity, and a mass kanalyzer unit for mass analysis of ions as produced by the negative corona discharge.
More specifically, in accordance with the invention as disclosed and claimed herein, the apparatus utilizes the inherent nature of some dangerous objects (typically certain organic chlorinated chemical compounds including, but not limited thereto, dioxin and nitro compounds) which tend to become negatively charged ions in a way such that negative corona discharge is used for ionization to produce negative ions or xe2x80x9canions,xe2x80x9d which are then subject to measurement by use of a mass spectrometer. Such anions due to the negative corona discharge are much higher than positive ions in production efficiency. This allows the detection sensitivity to increase accordingly. This in turn enables elimination of any troublesome and time-consuming pre-processing procedures which otherwise have been strictly required in the prior art.
The sample introduction unit includes a heatup module for use in heating a gas sample or samples up to predefined temperatures.
It should be noted that in order to efficiently perform generation of anions through negative corona discharge, it will be preferable that gas samples as introduced into the ion sources be set at high temperatures. Alternatively, it is recommendable to heat a corona discharging needle electrode used. Supposing that a gas sample is as high in temperature as about 100xc2x0 C. or more, water content contained in such gas sample also is vaporized permitting efficient ionization due to corona discharge with increased stability. The higher the needle electrode temperature, the lower the corona discharge initiation voltage. This results in an increase in corona discharge current even with the corona discharge voltage unchanged. This in turn causes the ion production efficiency to increase. In view of this, it will be effective to provide the heater module for use in increasing the gas sample temperature.
This heater module is disposed in the upstream of a gas sample inlet pump which is for introduction of the gas sample. The module is constituted from an inner pipe and an outer pipe. The inner pipe permits free passage of the gas sample therein. The outer pipe is outside of the inner pipe. The module also includes a heater for heating the gas sample introduced, which heater is between the inner and outer pipes. Alternatively, the heater module is in front of the gas sample inlet pump. If this is the case, this module is designed to have a xe2x80x9cdoublexe2x80x9d structure consisting essentially of an inner pipe for gas sample flow and an outer pipe residing outside of the inner pipe with a gas sample heater disposed inside of the inner pipe.
Still alternatively, the heater module may be laid out between the gas sample inlet pump and the corona discharge unit while employing a heater disposed in contact with the gas sample introduced, thereby causing this heater to heat the gas sample.
Product ions obtained in the corona discharge unit are then guided via one or more capillaries provided between the corona discharge unit and the mass analyzer unit to enter the mass analyzer for mass analyzation.
The corona discharge unit may include a mechanism for controlling the corona discharger so that its inside pressure is at a desired level. To this end, the corona discharge unit has an exit port for use in letting any excess or surplus gases residing within the corona discharge region escape to the outside. This residual gas exhaust port may be provided with a dead weight or sinker member less in weight for achievement of automated control of exhaust amount of surplus gases. Optionally, a gas valve is added thereto.
Providing the corona discharge region heatup module for ensuring that a sample retained at high temperatures undergoes the corona discharge makes it possible to obtain preferable results stated above.
Also preferably, use of an ion trap mass spectrometer as the pass analyzer results in a significant increase in detection sensitivity. This sensitivity increase may avoid the need for complicated and time-consuming pre-processing using the gas chromatography.
While a corona discharge region is typically at atmospheric pressure, this region may be designed to have an air-proof structure providing a sealed environment inside thereof for increasing the density or concentration of molecules residing therein, which leads to an ability to increase the ion productivity in such corona discharge region.
This method disclosed in Tandem Mass Spectrometry , F. W.McLafferty, John Wiley and Sons, Inc., p353-370, 1983 includes the steps of generating ions of M and/or (M-COCl) by using atmospheric pressure chemical ionization method with positive mode. However, this prior art is faced with a problem that ionization efficiency of dioxins and their related compounds is low. Dioxins and their related compounds. By using atmospheric pressure chemical ionization method with negative ion mode, the ionization efficiency of those compounds became higher because of their high electron affinities.
This method disclosed in U.S. Pat. No. 4,580,440 includes steps of a chemical concentration process, that is, collecting particulates and rapidly heating the collected particulates for achieving high sensitivity. However, the chemical concentration process is time-consuming whether for one measurement or continuous measurement. By using a physical concentration process based on an ion trap mass spectrometer, in which incident ions are trapped and concentrated with time, rapid measurement can be carried out.
The method disclosed in U.S. Pat. No. 4,718,268 includes steps of chemical concentration process, that is, collecting particulates, rapidly heating said collected particulates for achieving high sensitivity. However, the chemical cocentration process is time-consuming both for one measurement and continuous measurement. By using physical concentration process based on an ion trap mass spectrometer, in which incident ions are trapped and concentrated with time, rapid measurement can be carried out.